The present invention relates to apparatus and methods for monitoring and removing air or other gases from the blood.
Each year hundreds of thousands of people are afflicted with vascular diseases, such as arteriosclerosis, that result in cardiac ischemia. For more than thirty years, such disease, especially of the coronary arteries, has been treated using open surgical procedures, such as coronary artery bypass grafting. During such bypass grafting procedures, a sternotomy is performed to gain access to the pericardial sac, the patient is put on cardiopulmonary bypass, and the heart is stopped using a cardioplegia solution.
The development of minimally invasive techniques for cardiac bypass grafting, for example, by Heartport, Inc., Redwood City, Calif., and CardioThoracic Systems, Inc., Menlo Park, Calif., have placed a premium on reducing the size of equipment employed in the sterile field. Some previously known cardiopulmonary systems have attempted to miniaturize and integrate certain components of cardiopulmonary systems. U.S. Pat. Nos. 5,266,265 and 5,270,005, both to Raible, describe an extracorporeal blood oxygenation system having an integrated blood reservoir, an oxygenator formed from a static array of hollow fibers, a heat exchanger, a pump and a pump motor that is controlled by cable connected to a control console.
Concern over the entrainment of air in these, and conventional, blood handling systems led to the development of filtration designs with air venting capabilities. The placement of a filtration apparatus in the circuit as the final device to process the circulating blood before it is returned to the patient became the standard of care for cardiopulmonary bypass.
There exists a number of similar such filtration devices in clinical use. Many utilize a pleated element constructed of a woven fabric of a specified spacing to filter out particulate in a range of between 20 and 50 microns. U.S. Pat. No. 4,919,802 by Katsuri describes a pleated design that both filters and removes air from blood. Particulate matter of a size that exceeds the openings in the woven fabric is trapped and collected in the apparatus. The dimensions of the openings in the weave are subject to change, depending upon the amount of material and the pressure differential applied across the filter element.
The filter material of the Katsuri device is expected to deflect entrained air that is flowing tangential to the filter material, and to filter out bubbles that are greater in size than the filter material openings. The device includes a vent in its upper surface that enables air collected in the device to be vented to a venous reservoir. Because the venous reservoir typically operates at a lower pressure location in the circuit, flow from the vent location to the reservoir may be substantially continuous. Accordingly, air that enters the filtration apparatus is returned to, and ultimately vented from, the venous reservoir.
There are, however, a number of drawbacks attendant upon use of devices such as described in Katsuri. First, because the removal of air from the devices is through a vent either connected to a reservoir or alternative container, the pressure in the apparatus must be higher than the pressure in the reservoir or alternative container. Thus, it may be necessary to position the filter apparatus on the downstream, positive pressure side of a pump in a blood handling system. In addition, if the vent line is connected to a venous reservoir, a continuous flow of blood back to the reservoir is required to remove any air that may collect in the device. This return flow reduces or shunts the flow supplied to the patient and increases exposure of the blood to the foreign surfaces in the circuit. If a vacuum is applied to the open-air interface in the venous reservoir, the shunt flow is increased in proportion to the differential pressure.
Moreover, in most pleated designs, the pleated material forms a vertically oriented cylindrical tube that is potted at either end. The potting isolates the flow outside the pleated element from that inside of the pleated element. Air bubbles often become trapped underneath the upper potting, requiring the filter to be inverted to remove the bubbles, especially during the initial priming of the system.
In view of the limitations of previously known filtration systems, it would be desirable to provide a filter apparatus that monitors and removes gas for use, and methods of use, with an extracorporeal blood handling system.
It further would be desirable to provide a filter apparatus that monitors and removes gas, and methods of use, that permit one or more additional blood processing components, such as a heat exchanger, to be added to an extracorporeal blood circuit without having to prime the component prior to bringing that component online, thereby reducing disruption to operation of the blood handling system.
It also would be desirable to provide a filter apparatus that is capable of venting gas from the blood being processed without a shunt or loss of substantial blood from the flow supplied to the patient.
It still further would be desirable to provide a filter apparatus for monitoring and removing gas that can be disposed on the venous side of the extracorporeal circuit, either in conjunction with, or in place of, the venous reservoir.
In view of the foregoing, it is an object of the present invention to provide an apparatus and methods for filtering blood that monitors and removes air from an extracorporeal blood circuit to facilitate priming of the circuit and intraoperative use.
It is another object of the present invention to provide a filter apparatus that monitors and removes gas, and methods of uses, that permit one or more blood processing components, such as a heat exchanger, to be added to an extracorporeal blood circuit without having to prime the component prior to bringing that component online, thereby reducing disruption to operation of the blood handling system.
It is a further object of the present invention to provide a filter apparatus that is capable of venting gas from the blood being processed without a shunt or loss of substantial blood from the flow supplied to the patient.
It is yet another object of the present invention to provide a filter apparatus for monitoring and removing gas that can be disposed on the venous side of the extracorporeal circuit, either in conjunction with, or in place of, the venous reservoir.
These and other objects of the present invention are accomplished by providing a filter apparatus with a gas monitoring and removal system that removes air or other gases from the extracorporeal blood circuit. The apparatus of the present invention may be coupled to a conventional blood handling system, and may be initially primed with little or no saline or donor blood, with reduced risk of hemodilution. Moreover, additional components may be added to an existing extracorporeal circuit with little or no additional priming, and any air or other gases introduced into the system will be evacuated with no substantial impact on operation of a blood handling system.
In a preferred embodiment, a filter apparatus of the present invention monitors and removes gases from an extracorporeal blood circuit and comprises a housing having a gas collection plenum, a gas removal/blood filter, and a sensor positioned to sense gas within the interior of the housing to selectively remove gas. The gas removal/blood filter comprises a support structure that supports a screen-like material having an effective pore size between 20 and 250 microns. Alternatively, the gas removal/blood filter element may comprise a pleated filter material. Blood is introduced into the gas collection plenum via the blood inlet in a direction substantially tangential to the gas removal/blood filter to increase rotational velocity of the blood within the gas collection plenum, thereby enhancing separation of entrained gas.
Blood entering the housing via the blood inlet flows through the gas collection plenum, and air or other gases entrained in the blood are separated from the blood and collect in the gas collection plenum. A sensor disposed in communication with the gas collection plenum senses a parameter indicative of a level or volume of gas collected in the plenum, and selectively evacuates the plenum by coupling the plenum to a suction source, such as a standard operating room vacuum system. It is understood that if the placement of the filter apparatus is on the negative pressure side of the pump that the vacuum pressure must be regulated to be more negative than the pressure within the filter apparatus. Alternatively, if the filter apparatus is placed on the positive pressure side of the pump, the plenum may be simply connected to a container at atmospheric pressure. Blood that has been filtered exits the filter apparatus and passes to the rest of the blood handling system of the extracorporeal circuit.
Methods of operating the filter apparatus with the active gas removal system of the present invention also are provided.